1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device including a flexible thin film integrated circuit having a memory, a microprocessor (central processing unit, a CPU), or the like with a thin thickness like paper. The present invention further relates to a manufacturing method of a non-contact type thin film integrated circuit device including the thin film integrated circuit and an antenna, which is used for a card, a tag, a label, or the like to distinguish human, animals and plants, products, paper money, or the like mainly.
2. Description of the Related Art
In recent years, development of a semiconductor device which can transmit/receive data is actively advanced, and such a semiconductor device is called as an IC chip, an RF tag, a wireless tag, an electronic tag, a wireless processor, a wireless memory, or the like. Most semiconductor devices, which have been already put into practical use, are formed with single crystalline silicon substrates (hereinafter, referred to as IC chips in some case). Such semiconductor devices are frequently used in a product form such as a sheet type and a card type, and thus, required to be thin and flexible. Thus, a semiconductor element is thinned by grinding and polishing a backside of a base material.
Generally, the backside polish of a single crystalline silicon substrate including an integrated circuit is accomplished by final polishing with a loose grain after grinding with a whetstone, which is sometimes carried out in combination with etching with acid or alkal. The final thickness of the base material is required to be 100 μm or less to obtain a mirror-polished state, and a thickness of 500 μm or less is required for obtaining a sufficient flexibility. Development of thinner products become possible by polishing a semiconductor element thinner, and production technique is competed.
The element thinned by grinding and polishing is connected to an external antenna and sealed with a film or resin so that products such as a card and tag are manufactured. A built-in antenna type in which an antenna is formed directly over an element is sealed with a film or resin, and various products can be manufactured. In this manner, an IC chip can be used in various ways without limitation on its application, by making its final state thin and flexible.
The step of polishing the conventional IC card is described in the Patent Document 1 below.
It is possible to manufacture a thin semiconductor element by grinding and polishing a base material in order to obtain a non-single crystalline silicon thin film transistor circuit which is manufactured over an insulating substrate such as a glass substrate, in addition to an integrated circuit over a single crystalline silicon substrate. The non-single crystalline silicon thin film transistor can be formed over a large and inexpensive glass substrate, and manufacturing cost can be reduced considerably compared with a semiconductor element using a single crystalline silicon wafer.
[Patent Document 1] Japanese Patent Laid-Open No. Hei3-87299
However, there are various restrictions on the shape, step, or the like in the case of manufacturing a thin element using a glass substrate as a base material. As a glass substrate used as a base material, a non-polished substrate manufactured by a fusion method is generally used in order to reduce a manufacturing cost. Polishing is necessary for a glass substrate manufactured by a float process; however, only one side is polished for reducing cost. Thus, since there is variation in a thickness in the range from several μm to several ten μm on one or both sides of a glass substrate, variation in the thickness of a substrate surface is generated in thinning process of 100 μm or less with polishing. Thus, yield of the element is lowered.
On the other hand, variation in a substrate thickness is less likely to be generated if a substrate of which both surfaces are polished is used. However, it is difficult to prepare a large apparatus in accordance with a large glass substrate or to polish a large substrate uniformly. Thus, there is a problem such that cost reduction in a step using a small single crystalline silicon substrate or a quartz substrate cannot be achieved.
In the same manner, even if a small substrate of which both surfaces are polished is used, the number of products manufactured per unit area reduces. Thus, cost tends to increase. In addition, a substrate having corners is unsuitable for a grinding and polishing apparatus having a rotational friction structure, and there is a problem such that a corner defect and crack is easily produced. Therefore, a round substrate having an excellent symmetric as a single crystalline substrate is preferable for a rotational friction structure; however, cost tends to increase when a glass substrate is processed into a round shape.
Therefore, it is very difficult to manufacture a non-single crystalline silicon thin film transistor element over a glass substrate having a thickness of 100 μm or less at low cost and high yield. Thus, development of a product with a thin element using an inexpensive glass substrate as a base material cannot be carried out, and a thin element using an expensive single crystalline silicon substrate as a base material is used for a product at present. As a result, expansion of markets is suppressed.
In the case where a glass substrate is used, since its melting point is a rate-controlling point, it is generally manufactured with a low temperature process of 600° C. or less. For example, the temperature is limited for a field effect polysilicon thin film transistor manufactured with a glass substrate, in a process of crystallization and activation of a polysilicon layer to be an active layer and in a process where a high temperature is advantageous for forming a gate oxide film, or the like. Thus, there has been a problem such that electric properties are deteriorated compared with a field effect transistor manufactured with a single crystalline silicon substrate or a quartz substrate.